Dear Vaagmiji
I could be still missing the point and whatever I write here may not be the right response for your question. But thanks for that question.
If the substrate/canvass that you are talking about is the 'surface' on which energy moves, then it is spacetime, which I call as Hiranyagarbha. According to standard model, this Hiranyagarbha (spacetime) expanded immediately after Big-Bang in 'cosmic inflation epoch' (analogy is balloon filled with air expanding greatly). This inflated spacetime is the 'Brahma'.
Like the Puranas that say that svayambhu established primordial waters, created the initial seed, entered into it and the seed became the Hiranya-garbha in which Universe evolves, Standard model today says that after Big-Bang energy(may be something more than energy whose nature we don't know today) and spacetime (seed) got established first and then the spacetime expanded greatly, became the 'womb' in which Universal matter evolves.
hiraṇyagarbhaḥ samavartatāgre bhūtasya jātaḥ patirekāsīt (before time of matter/beings existed Lord Hiranyagarbha)
sa dādhāra pṛthvīṃ dhyāmutemāṃ kasmai devāyahaviṣā vidhema (gives, bears all the prthvi, dyaus ; for/to whom we offer the oblations).
This four dimensional Hiranyagarbha or spacetime is the surface that gives and bears the Universe. On it the 'rudras' or 'force-fields' manifest. It is in these rudras or force-fields that energy, mass and particles that make the Universe manifests. It is the interaction of these force-fields filled with energy and mass (impeding motion) that complex matter forms.
The evolution of Universe is a Yajna or sacrifice. One form of matter is sacrificed (offered as oblations, havis) to build more complex forms of matter. All the oblations/offerings in this Yajna are offered to this Hiranyagarbha, the spacetime, as it is what holds all the matter and bears the Yajna.
The Brahma (expanded spacetime) bends to the 'energy' or shiva (and also vishnu or mass) and hence is called 'Ka-ancha'. This is called warping of spacetime, which we perceive as 'gravity'.
What is the nature of this Hiranyagarbha or four-dimensional spacetime..?
From a science view, we don't know much about it except that the three dimensional space and whatever we perceive as time are actually a continuum and are in fact a four dimensional spacetime. We also know that there is Cold Dark Matter in the Universe which is nearly 2/3rd of overall mass of Universe (similar to the Purusha desribed in vedas). In fact I map Purusha to this cold dark matter.
But if my understanding of Vedas and Upanishads and their mappings to science is right, then Brahma bloomed from the navel of Narayana.
Narayana is Maha-Vishnu. Vishnu (Higgs field) and Purusha (Dark matter). Probably there is a Unified field of Higgs and Dark Matter (which is the Naryana) (such theories are being discussed now), during the Big-Bang. Shortly after Big-Bang in which huge energy got released, during the cosmic inflation epoch, the Unified field separated and Higgs field expanded greatly causing the expansion of spacetime. The inflated spacetime (Brahma) is filled with Purusha or dark matter. That's how that Narayana is said to have created the seed and also entered in it making it a womb.
That cosmic inflation could have been driven by Higgs field or a unified field related to Higgs is my supposition from the reading of vedic texts. It is psuedo-science at this point. Whether we believe the Puranas that say Brahma bloomed out of Maha-Vishnu or not, current models indicate that spacetime indeed expanded greatly, shortly after the Big-Bang. May be I am totally wrong.
Purusha, the cold dark matter is the 'bed' on which the Universe evolves according to the vedic texts. Its role is to protect the Yajna or sacrifice or evolution of Universe and its matter.
I can go one more step and propose that Brahma is not four dimensional, but five dimensional. The fifth head of Brahma or fifth dimension is plucked out by expanding energy/Shiva (as kAla Bhairava). Hence fifth dimension remains a shortened dimension causing probably quantum entanglement. Einstein had actually proposed a shortened fifth dimension, but did not work out the mathematics for it.
What is behind this Narayana (Unified field of Dark matter and Higgs) and Shiva (energy) and Brahma (spacetime) is referred to as 'Atma' at several places. I translate Atman as At-manas. Nara are real particles, that are on-shell, that satisfy energy-momentum relationship, that obey the Universal laws that exist today. 'Manas' are virtual particles that are off-the-shell, that do not obey the Universal laws. They are 'virtual' because they are our theoretical models and cannot be proved to exist. But without this virtual particles, our understanding of Universe is not complete. We need them to 'bind' the real particles in our models at different places.
If manas is virtual, At-manas is extremely virtual. From this extremely virtual Atman, it seems that whatever we perceive as shiva, narayana, Hiranyagarbha seems to have come.
Some people call this Atma, Narayana or Maha-Vishnu himself. Some people like to call it Shiva himself. Some people like to call it Shakti. Some people say at all times in Universe it is only force-fields (Rudra) that existed. Hence Atma is an Unified force-field (a Rudra) in which everything is extremely virtual and post Big-Bang it started spewing real particles.
Because it is extremely virtual and its nature not known or can only be partially known, we can identify it with anything that we perceive and we won't be able to fully identify with anything we perceive. The physics of the very early Universe or what was before Big Bang is different from the physics of Universe post the Big-Bang. Hence we may not know what it is for sure or we may get to know only partly.
That's exactly what Nasadiya suktam says.
As far as concept of sunyavada is concerned, science says today, even in complete vacuum exists all the force-fields with some energy and can pop out particles/anti-particles from vacuum.
So it depends on upto what point you investigate or which way you want to investigate.
-TBT
